For the longest time, the pro AV industry was characterized by proprietary cabling formats: One piece of coax with BNCs (or yellow RCA plugs) for composite video. A 15-pin DB9 connector for VGA. DIN connectors for S-video. And RJ-45 plugs for twisted-pair analog signal extenders.
With the advent of digital signal interfacing, we’ve got a slew of new connectors that look nothing like their predecessors: The 19-pin HDMI plug. The 20-pin DisplayPort plug. Micro USB. Type-C USB. DVI. And RJ-45 plugs for twisted-pair digital signal extenders.
Wait – what? We’re still using RJ-45 plugs, and category wire? Apparently, and we’ve now migrated to the more robust category 6 wire (rated for 1GigE connections); more often than not equipped with shielding to minimize crosstalk and ground wires for longer signal transmission distances.
The thing is; we’re now facing a new set of challenges in the way we multiplex and transport video, audio, RS232, IR, USB, metadata, and even power. One camp advocates for using a proprietary system (HDBaseT) that currently has a practical limit of about 330 feet and is still limited to supporting the older HDMI 1.4 standard. But it transports uncompressed signals and is very popular in the InfoComm world.
The other camp is advocating that we compress and convert all video/audio/data to packets and transmit them with IP headers through conventional networks. This method increases transmission distance considerably and can run over copper or optical fiber (or even coax, for that matter), through conventional, open-system network switches. This approach is favored by telecom companies, along with broadcast networks, IPTV services, and other multichannel video system operators.
Now, another camp says that they’ve developed a “better mousetrap” for doing AV-over-IP, using a low-latency protocol known as BlueRiver NT that uses light compression on video and audio.
So which is the way to go? That’s not an easy question to answer, but the most common approach to transmitting digital video and audio over long distances is solution #2, using MPEG compression and standard IP protocols to transport video and audio through everyday networks and switches.
What’s more; it’s likely to stay that way. While the HDBaseT format works very well, it is based on a proprietary pulse-amplitude modulation (PAM) scheme that requires chipsets manufactured by Valens Semiconductor. And there is that distance limitation, although support for optical fiber is now in the standard. But you can’t run HDBaseT signals through conventional network switches.
The BlueRiver NT approach (designed by AptoVision) claims to improve on conventional AV-over-IP transmission while retaining low latency with Adaptive Clock Re-synchronization. This technique interleaves audio, video, 1GB Ethernet and other signals with an embedded clocking mechanism.
According to AptoVision, this approach recovers the clocks for both audio and video at the decoder end with only a few lines of latency while remaining fully synched to the source clock across the entire network; even through switches. The light compression cranks down data rates by 50% with a “lossless” two-step codec.
While you can run BlueRiver NT-coded video and audio through conventional IP networks and switches, you must use their proprietary codec in transmitters and receivers. So it’s not a true “open” system, although it is more flexible than HDBaseT for installation in a network environment.
So, back to conventional AV-over-IP, which (come to think of it) isn’t really that “conventional” nowadays. Thanks to the new HEVC H.265 codec and a series of real-time protocols, it’s now possible to stream 1080p content with conventional IP headers through any network and switch and decode it with any H.265-compatible device, like a set-top box or media player, or even a new Ultra HDTV.
And your 1080p content can travel through networks at speeds as slow as 1 to 2 megabits per second, yet still yield good image quality when decoded. Compare that to the current 6 – 10 Mb/s requirement for 1080p/60 using H.264 AVC coding, and you’re seeing quite an improvement.
H.265 decoder chips are now widely available from Broadcom, which means that a whole host of displays and media players can be used to decode AV-over-IP signals – you aren’t stuck with a proprietary system. What’s more, AV-over-IP systems aren’t restricted by bandwidth in their transmitters and receivers. If the network can handle 1 Gb/s of data, so be it. And if you are fortunate enough to tie into a 10GigE network with optical fiber, the sky’s the limit!
Now, none of what I just wrote says these systems can’t co-exist. It may make sense to use HDBaseT extenders (or BlueRiver NT versions) to connect from a decoder to distant displays. Or, the input of an encoder could be fed by an HDBaseT / BlueRiver receiver.
The advantage of a 100% AV-over-IP system is that it nicely sidesteps the current speed limit problems we’re experiencing with HDMI, and to a lesser extent, DisplayPort. We’ve reduced the video and audio signals to a baseband format and compressed them into packets, which can travel through ANY manufacturer’s IP switching and routing gear.
Best of all, the addressing is done in software with IP addresses, which helps manage the size of the switch and ensures it is always easily scalable. If you didn’t specify enough inputs and outputs on a matrix switch for HDMI, you’ve got a problem! But if you need to connect more displays through an AV-over-IP system, you just need more IP addresses.
In the near future, you can count on hearing plenty of debates about which of these formats is “the way to go” for digital signal distribution. HDBaseT is widely entrenched in the commercial AV world (and to some extent, in home theater). But it’s not popular with IT-savvy users, where conventional MPEG/AES and IP headers rule the day.
And it remains to be seen how much traction BlueRiver NT can gain in the pro AV space. Some manufacturers are already supporting this format as a better way to do AV-over-IP than H.265. Latency issues with any video codec are largely a result of both compression and forward error correction, and we’re still in the early stages of H.265 adoption. So it’s a little too early to pick winners and losers here.
Frankly; if I was designing a high-performance video network, I’d use 100% optical fiber cabling and H.265/IP to get the job done, running everything through 1GigE or (if the budget permitted) 10GigE switches and using fiber-to-“whatever” receivers/converters at all terminations.
That would essentially guarantee future-proofing of the installation, as all I’d need to do to connect an upgraded interface would be to swap out a plug-in card or install a low-cost black box as needed.
But that’s just me…
Posted by Pete Putman, July 16, 2015 2:18 PM
About Pete PutmanPeter Putman is the president of ROAM Consulting L.L.C. His company provides training, marketing communications, and product testing/development services to manufacturers, dealers, and end-users of displays, display interfaces, and related products.
Pete edits and publishes HDTVexpert.com, a Web blog focused on digital TV, HDTV, and display technologies. He is also a columnist for Pro AV magazine, the leading trade publication for commercial AV systems integrators.